/*
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * This software is open source.
 * See the bottom of this file for the licence.
 */

package com.googlecode.bluetools.dom4j.tree;

import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.util.Map;

import com.googlecode.bluetools.dom4j.Namespace;

/**
 * <p>
 * <code>NamespaceCache</code> caches instances of <code>DefaultNamespace</code> for reuse both across documents and
 * within documents.
 * </p>
 * 
 * @author <a href="mailto:james.strachan@metastuff.com">James Strachan </a>
 * @author Maarten Coene
 * @author Brett Finnell
 * @version $Revision: 1.1 $
 */
public class NamespaceCache {
	private static final String CONCURRENTREADERHASHMAP_CLASS = "EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap";

	/**
	 * Cache of {@link Map}instances indexed by URI which contain caches of {@link Namespace}for each prefix
	 */
	protected static Map cache;

	/**
	 * Cache of {@link Namespace}instances indexed by URI for default namespaces with no prefixes
	 */
	protected static Map noPrefixCache;

	static {
		/* Try the java.util.concurrent.ConcurrentHashMap first. */
		try {
			Class clazz = Class.forName("java.util.concurrent.ConcurrentHashMap");
			Constructor construct = clazz.getConstructor(new Class[] {
					Integer.TYPE,
					Float.TYPE,
					Integer.TYPE
			});
			cache = (Map) construct.newInstance(new Object[] {
					new Integer(11),
					new Float(0.75f),
					new Integer(1)
			});
			noPrefixCache = (Map) construct.newInstance(new Object[] {
					new Integer(11),
					new Float(0.75f),
					new Integer(1)
			});
		}
		catch (Throwable t1) {
			/* Try to use the util.concurrent library (if in classpath) */
			try {
				Class clazz = Class.forName(CONCURRENTREADERHASHMAP_CLASS);
				cache = (Map) clazz.newInstance();
				noPrefixCache = (Map) clazz.newInstance();
			}
			catch (Throwable t2) {
				/* If previous implementations fail, use internal one */
				cache = new ConcurrentReaderHashMap();
				noPrefixCache = new ConcurrentReaderHashMap();
			}
		}
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @param prefix DOCUMENT ME!
	 * @param uri DOCUMENT ME!
	 * 
	 * @return the namespace for the given prefix and uri
	 */
	public Namespace get(String prefix, String uri) {
		Map uriCache = getURICache(uri);
		WeakReference ref = (WeakReference) uriCache.get(prefix);
		Namespace answer = null;

		if (ref != null) {
			answer = (Namespace) ref.get();
		}

		if (answer == null) {
			synchronized (uriCache) {
				ref = (WeakReference) uriCache.get(prefix);

				if (ref != null) {
					answer = (Namespace) ref.get();
				}

				if (answer == null) {
					answer = createNamespace(prefix, uri);
					uriCache.put(prefix, new WeakReference(answer));
				}
			}
		}

		return answer;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @param uri DOCUMENT ME!
	 * 
	 * @return the name model for the given name and namepsace
	 */
	public Namespace get(String uri) {
		WeakReference ref = (WeakReference) noPrefixCache.get(uri);
		Namespace answer = null;

		if (ref != null) {
			answer = (Namespace) ref.get();
		}

		if (answer == null) {
			synchronized (noPrefixCache) {
				ref = (WeakReference) noPrefixCache.get(uri);

				if (ref != null) {
					answer = (Namespace) ref.get();
				}

				if (answer == null) {
					answer = createNamespace("", uri);
					noPrefixCache.put(uri, new WeakReference(answer));
				}
			}
		}

		return answer;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @param uri DOCUMENT ME!
	 * 
	 * @return the cache for the given namespace URI. If one does not currently exist it is created.
	 */
	protected Map getURICache(String uri) {
		Map answer = (Map) cache.get(uri);

		if (answer == null) {
			synchronized (cache) {
				answer = (Map) cache.get(uri);

				if (answer == null) {
					answer = new ConcurrentReaderHashMap();
					cache.put(uri, answer);
				}
			}
		}

		return answer;
	}

	/**
	 * A factory method to create {@link Namespace}instance
	 * 
	 * @param prefix DOCUMENT ME!
	 * @param uri DOCUMENT ME!
	 * 
	 * @return a newly created {@link Namespace}instance.
	 */
	protected Namespace createNamespace(String prefix, String uri) {
		return new Namespace(prefix, uri);
	}
}

/*
 * Redistribution and use of this software and associated documentation ("Software"), with or without modification, are
 * permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain copyright statements and notices. Redistributions must also contain a
 * copy of this document.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
 * following disclaimer in the documentation and/or other materials provided with the distribution.
 * 
 * 3. The name "DOM4J" must not be used to endorse or promote products derived from this Software without prior written
 * permission of MetaStuff, Ltd. For written permission, please contact dom4j-info@metastuff.com.
 * 
 * 4. Products derived from this Software may not be called "DOM4J" nor may "DOM4J" appear in their names without prior
 * written permission of MetaStuff, Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
 * 
 * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
 * 
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 */
